U.S. patent application number 10/561253 was filed with the patent office on 2006-06-29 for polymerization initated at sidewalls of carbon nanotubes.
Invention is credited to Jared L. Hudson, Ramanan Krishnamoorti, Cynthia A. Mitchell, James M. Tour, Koray Yurekli.
Application Number | 20060142466 10/561253 |
Document ID | / |
Family ID | 34392894 |
Filed Date | 2006-06-29 |
United States Patent
Application |
20060142466 |
Kind Code |
A1 |
Tour; James M. ; et
al. |
June 29, 2006 |
Polymerization initated at sidewalls of carbon nanotubes
Abstract
The present invention is directed to aryl halide (such as aryl
bromide) functionalized carbon nanotubes can be utilized in anionic
polymerization processes to form polymer-carbon nanotube materials
with improved dispersion ability in polymer matrices. In this
process the aryl halide is reacted with an alkyllithium species or
is reacted with a metal to replace the aryl-bromine bond with an
aryl-lithium or aryl-metal bond, respectively. It has further been
discovered that other functionalized carbon nanotubes, after
deprotonation with a deprotonation agent, can similarly be utilized
in anionic polymerization processes to form polymer-carbon nanotube
materials. Additionally or alternatively, a ring opening
polymerization process can be performed. The resultant materials
can be used by themselves due to their enhanced strength and
reinforcement ability when compared to their unbound polymer
analogs. Additionally, these materials can also be blended with
pre-formed polymers to establish compatibility and enhanced
dispersion of nanotubes in otherwise hard to disperse matrices
resulting in significantly improved material properties. The
resultant polymer-carbon nanotube materials can also be used in
drug delivery processes due to their improved dispersion ability
and biodegradability, and can also be used for scaffolding to
promote cellular growth of tissue.
Inventors: |
Tour; James M.; (Bellaire,
TX) ; Hudson; Jared L.; (Houston, TX) ;
Krishnamoorti; Ramanan; (Bellaire, TX) ; Yurekli;
Koray; (Cengelkoy, TR) ; Mitchell; Cynthia A.;
(Houston, TX) |
Correspondence
Address: |
Robert C Shaddox;Winstead Sechrest Minick
PO Box 50784
Dallas
TX
75201
US
|
Family ID: |
34392894 |
Appl. No.: |
10/561253 |
Filed: |
June 21, 2004 |
PCT Filed: |
June 21, 2004 |
PCT NO: |
PCT/US04/19769 |
371 Date: |
December 19, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60480348 |
Jun 20, 2003 |
|
|
|
Current U.S.
Class: |
524/495 ;
977/902 |
Current CPC
Class: |
C01B 32/174 20170801;
C08K 9/04 20130101; C01B 2202/02 20130101; C08F 292/00 20130101;
C08K 3/041 20170501; C08F 112/08 20130101; C08F 4/484 20130101;
B82Y 30/00 20130101; B82Y 40/00 20130101; C08F 2/00 20130101; C08F
112/08 20130101; C08F 4/484 20130101; C08K 3/041 20170501; C08L
25/06 20130101; C08K 3/041 20170501; C08L 67/04 20130101 |
Class at
Publication: |
524/495 ;
977/902 |
International
Class: |
C08K 3/04 20060101
C08K003/04 |
Goverment Interests
[0002] This invention was made with support from the National
Aeronautics and Space Administration, Grant Nos. NASA-JSC-NCC-9-77
and TEES 68371, passed through from NASA-URETI NCC-01-0203; the
National Science Foundation, Grant No. NSR-DMR-0073046; and the
U.S. Air Force Office of Scientific Research, Grant No.
F49620-01-0364.
Claims
1. A method comprising: a) providing functionalized carbon
nanotubes, wherein the functionalized carbon nanotubes comprise a
functionalized species on the sidewall of the carbon nanotubes
selected from the group consisting of (i) aryl halide
functionalized carbon nanotubes and (ii) specie comprising a
nucleation site operable for anionic or ring opening
polymerization; b) dispersing said aryl halide functonalized carbon
nanotubes in a solvent; c) adding to the solvent at least one of:
(i) an alkyllithium species, wherein the alkylthium species reacts
with the aryl halide functionalized carbon nanotubes (ii) a metal,
wherein the metal reacts with the aryl halide functionalized carbon
nanotubes and replaces aryl-halide bonds with aryl-metal bonds,
(iii) a deprotonating agent, wherein the deprotonating agent
deprotonates the nucleation sites of the functionalized carbon
nanotubes and form initiator groups for the anionic or ring opening
polymerization; d) adding a monomer to the solvent; and e)
initiating anionic or ring opening polymerization utilizing the
monomer and the functionalized carbon nanotubes to form a
polymer-carbon nanotube material.
2. A method comprising: a) providing aryl halide functionalized
carbon nanotubes; b) dispersing said aryl halide functionalized
carbon nanotubes in a solvent; c) adding an alkyllithium species to
the solvent, wherein the alkylthium species reacts with the aryl
halide functionalized carbon nanotubes; d) adding a monomer to the
solvent; and e) initiating anionic or ring opening polymerization
utilizing the monomer and the functionalized carbon nanotubes to
form a polymer-carbon nanotube material.
3. A method comprising: a) providing aryl halide functionalized
carbon nanotubes; b) dispersing the aryl halide functionalized
carbon nanotubes in a solvent; c) adding a metal to the solvent,
wherein the metal reacts with the aryl halide functionalized carbon
nanotubes and replaces aryl-halide bonds with aryl-metal bonds; d)
adding a monomer to the solvent; and e) initiating anionic or ring
opening polymerization utilizing the monomer and the functionalized
carbon nanotubes to form a polymer-carbon nanotube material.
4. The method of claim 3, wherein the metal comprises a substance
selected from the group consisting of include zinc, nickel,
potassium, sodium, lithium, magnesium, cesium, palladium, and
combinations thereof.
5. The method of claim 3, wherein the metal is Mg, which reaction
with the aryl-halide functionalized carbon nanotubes comprises
formation of a Grignard species.
6. The method of claims 1-4 or 5, wherein the carbon nanotubes have
the aryl halides bonded to the sidewall of the carbon
nanotubes.
7. The methods of claims 1-4 or 5, wherein the aryl halide
comprises a halide selected from the group consisting of chlorine,
bromine, iodine, and combinations thereof.
8. The methods of claims 1-4 or 5, wherein the aryl halide is aryl
bromide.
9. The methods of claims 1-4, or 5, wherein the alkyllithium
species is n-butyllithium.
10. A method comprising: a) providing functionalized carbon
nanotubes, wherein the specie functionalized on the carbon
nanotubes comprise at least one initiation site operable for
anionic or ring opening polymerization; b) dispersing the
functionalized carbon nanotubes in a solvent; c) adding a
deprotonating agent to the solvent, wherein the deprotonating agent
deprotonate the nucleation sites of the functionalized carbon
nanotubes and form initiator groups for the anionic or ring opening
polymerization; d) adding a monomer to the solvent; and e)
initiating anionic or ring opening polymerization utilizing the
monomer and the functonalized carbon nanotubes to form a
polymer-carbon nanotube material.
11. The method of claim 10, wherein the nucleation sites of the
functonalized carbon nanotubes are at least one of the elements
selected from group consisting of carbon, sulfur, oxygen, and
nitrogen.
12. The method of claim 10, wherein the functionalized carbon
nanotubes are selected from the group consisting of phenol
functionalized carbon nanotubes, thiophenol functionalized carbon
nanotubes, phenethyl alcohol functionalized nanotubes
(CNT-C.sub.6H.sub.4--CH.sub.2CH.sub.2OH),
CNT-C.sub.6H.sub.4--NHBoc, and combinations thereof.
13. The method of claims 10-11 or 12, wherein the species
functionalized on the carbon nanotubes is functonalized on the
sidewall of the carbon nanotubes
14. The method of claims 10-11 or 12, wherein the deprotonating
agent comprises a base.
15. The method of claim 14, wherein the base is selected from the
group consisting of KOH, KH, NaOH, NaH, and potassium
hexamethyidisilazide.
16. The method of claims 10-11 or 12, wherein the deprotonating
agent comprises a metal operable for deprotonating the nucleation
sites.
17. The method of claim 16, wherein the metal is selected from the
group consisting of zinc, nickel, potassium, sodium, lithium,
magnesium, cesium, palladium, and combinations thereof.
18. The methods of claims 1-5, 10-11, or 12, wherein the initiating
anionic or ring opening polymerization step comprises initiating
anionic polymerization to form the polymer-carbon nanotube
material.
19. The methods of claims 1-5, 10-11, or 12, wherein the initiating
anionic or ring opening polymerization step comprises initiating
ring opening polymerization to form the polymer-carbon nanotube
material.
20. The methods of claims 1-5, 10-11 or 12, wherein the
functionalized carbon nanotubes are single-wall carbon
nanotubes.
21. The methods of claims 2-5, 10-11 or 12, wherein the solvent is
tetrahydrofuran.
22. The methods of claims 2-5, 10-11 or 12, wherein the monomer is
selected from the group consisting of styrene, acrylates, methyl
acrylates, vinyl acetate, vinyl pyridines, isoprene, butadiene,
chloroprene, acrylonitrile, maleic anhydride, and combinations
thereof.
23. The methods of claims 2-5, 10-11 or 12, wherein the monomer
comprises styrene.
24. The methods of claims 2-5, 10-11 or 12, further comprising
adding a suitable terminating agent for terminating the anionic or
ring opening polymerization process.
25. The method of claim 24, wherein the terminating agent is
selected from the group consisting of ethanol, acetaldehyde,
trimethylsilyl chloride, and combinations thereof.
26. The method of claim 24, wherein the terminating agent is
ethanol.
27. The methods of claims 1-5, 10-11 or 12, wherein concentration
of the monomer is in the range between about 0.03 and about 0.16
g/ml.
28. The methods of claims 1-5, 10-11 or 12, wherein the step of
initiating anionic polymerization occurs at a temperature in the
range between about 0.degree. C. and about 50.degree. C.
29. The methods of claims 1-5, 10-11 or 12, wherein average chain
length of the polymer bonded the carbon nanotubes in the
polymer-carbon nanotube material is in the range between about 5
and about 1 million,
30. The method of claim 29, wherein the average chain length is
between about 1000 and about 1 million.
31. The methods of claims 1-5, 10-11 or 12, wherein a catalyst is
used during the step of initiating anionic or ring opening
polymerization.
32. The method of claim 31, wherein the catalyst comprises
TiCl.sub.4.
33. The method of claims 1-5, 10-11 or 12 further comprising the
step of utilizing the polymer-carbon nanotube material in a drug
delivery process.
34. The method of claims 1-5, 10-11 or 12, further comprising the
step of utilizing the polymer-carbon nanotube material for
scaffolding to promote cellular tissue growth.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This Application claims priority to U.S. Provisional Patent
Application Ser. No. 60/480,348 filed Jun. 20, 2003.
FIELD OF THE INVENTION
[0003] The present invention relates generally to processes for
growing polymer chains via anionic polymerization, and/or
alternatively via ring opening polymerization, from the sidewalls
of functionalized carbon nanotubes, which will facilitate greater
dispersion in polymer matrices and greatly enhanced reinforcement
ability in polymeric material.
BACKGROUND
[0004] Fullerenes are closed-cage molecules composed entirely of
sp.sup.2-hybridized carbons, arranged in hexagons and pentagons.
Fullerenes (e.g., C.sub.60) were first identified as closed
spheroidal cages produced by condensation from vaporized carbon.
Fullerene tubes are produced in carbon deposits on the cathode in
carbon arc methods of producing spheroidal fullerenes from
vaporized carbon. Ebbesen et al., Nature, 1992, 358:220 and Ebbesen
et al., Annual Review of Materials Science, 1994, 24:235-264. Such
tubes are referred to herein as carbon nanotubes. Many of the
carbon nanotubes made by these processes were multi-wall nanotubes
(MWNTs), i.e., the carbon nanotubes resembled concentric cylinders
having multiple walls or shells arranged in a manner which can be
considered analogous to Russian "nesting dolls." Carbon nanotubes
having up to seven walls have been described in the prior art
(Ebbesen et al., Annual Review of Materials Science, 1994,
24:235-264; Iijima et al., Nature, 1991, 354:56-58).
[0005] Single-wall carbon nanotubes (SWNTs) were discovered in 1993
in soot produced in an arc discharge in the presence of transition
metal catalysts. Such SWNTS, comprised of a single tube of carbon
atoms, are the smallest of the carbon nanotubes. SWNTs can
typically have lengths of up to several micrometers
(millimeter-long nanotubes have been observed) and diameters of
approximately 0.5 nm-10.0 nm (Saito et al., Physical Properties of
Carbon Nanotubes, 1998, London: Imperial College Press; Sun et al.,
Nature, 2000, 403:384), although most have diameters of less than 2
nm (Saito et al.). Diameters as small as 0.4 nm have been reported,
but these were formed inside either MWNTs (Qin et al., Chem. Phys.
Lett., 2001, 349:389-393) or zeolites (Wang et al., Nature, 2000,
408:50-51). SWNTs, and carbon nanotubes of all types have since
been produced by other techniques which include chemical vapor
deposition techniques (Hafner et al., Chem. Phys. Lett., 1998,
296:195-202; Cheng et al., Chem. Phys. Lett., 1998, 289:602-610;
Nikolaev et al., Chem. Phys. Lett., 1999, 313:91-97), laser
ablation techniques (Thess et al., Science, 1996, 273:483-487), and
flame synthesis (Vander Wal et al., J. Phys. Chem. B., 2001,
105(42):10249-10256).
[0006] Since their discovery, there has been a great deal of
interest in the functionalization (sometimes referred to as
derivatization) of carbon nanotubes and, more particularly, in
single-wall carbon nanotubes, to facilitate their manipulation, to
enhance the solubility of such nanotubes, and to make the nanotubes
more amenable to blend and composite formation. This is because
single-wall carbon nanotubes are one of the more striking
discoveries in the chemistry and materials genre in recent years.
Nanotubes posses tremendous strength, an extreme aspect ratio, and
are excellent thermal and electrical conductors. A plethora of
potential applications for nanotubes have been hypothesized, and
some progress is being made towards commercial applications.
Accordingly, chemical modification of single-wall carbon nanotubes,
as well as multi-wall carbon nanotubes, will be necessary for some
applications. For instance, such applications may require grafting
of moieties to the nanotubes: to allow assembly of modified
nanotubes, such as single-wall carbon nanotubes, onto surfaces for
electronics applications; to allow reaction with host matrices in
polymer blends and composites; and to allow the presence of a
variety of functional groups bound to the nanotubes, such as
single-wall carbon nanotubes, for sensing applications. And once
blended, some applications may benefit from the thermal removal of
these chemical moieties, as described in PCT publication WO
02/060812 by Tour et at, filed Jan. 29, 2002 and incorporated by
reference herein.
[0007] While there have been many reports and review articles on
the production and physical properties of carbon nanotubes, reports
on chemical manipulation of nanotubes have been slow to emerge.
There have been reports of functionalizing nanotube ends with
carboxylic groups (Rao, et at, Chem. Commun., 1996,1525-1526; Wong,
et at, Nature, 1998, 394:52-55), and then further manipulation to
tether them to gold particles via thiol linkages (Liu, et at,
Science, 1998, 280:1253-1256). Haddon and co-workers (Chen, et at,
Science, 1998, 282:95-98) have reported solvating single-wall
carbon nanotubes by adding octadecylamine groups on the ends of the
tubes and then adding dichlorocarbenes to the nanotube sidewall,
albeit in relatively low quantities (.about.2%).
[0008] Success at covalent sidewall derivatization of single-wall
carbon nanotubes has been limited in scope, and the reactivity of
the sidewalls has been compared to the reactivity of the basal
plane of graphite. Aihara, J. Phys. Chem. 1994, 98:9773-9776. A
viable route to direct sidewall functionalization of single-wall
carbon nanotubes has been fluorination at elevated temperatures,
which process was disclosed in a patent commonly assigned to the
assignee of the present Application, U.S. Pat. No. 6,645,455,
"Chemical Derivatization Of Single-Wall Carbon Nanotubes To
Facilitate Solvation Thereof; And Use Of Derivatized Nanotubes To
Form Catalyst-Containing Seed Materials For Use In Making Carbon
Fibers," to Margrave et at, issued Nov. 11, 2003. These
functonalized nanotubes may either be de-fluorinated by treatment
with hydrazine or allowed to react with strong nucleophiles, such
as alkyllithium reagents. Although fluorinated nanotubes may well
provide access to a variety of functionalized materials, the
two-step protocol and functional group intolerance to organolithium
reagents may render such processes incompatible with certain,
ultimate uses of the carbon nanotubes. Other attempts at sidewall
modification have been hampered by the presence of significant
graphitic or amorphous carbon contaminants. Chen, Y. et al., J.
Mater Res. 1998, 13:2423-2431. For some reviews on sidewall
functionalization, see Bahr et al., J. Mater. Chem., 2002, 12:1952;
Banerjee et al., Chem. Eur. J., 2003, 9:1898; and Holzinger et al.,
Angew. Chem. Int. Ed., 2001, 40(21):4002-4005. Within the
literature concerning sidewall-functionalization of SWNTs, however,
there is a wide discrepancy of solubility values between reports.
This is due to explicable variations in filtration methods.
[0009] A more direct approach to high degrees of functionalization
of nanotubes (i.e., a one step approach and one that is compatible
with certain, ultimate uses of the nanotubes) has been developed
using diazonium salts and was disclosed in a co-pending application
commonly assigned to the assignee of the present Application. See
PCT publication WO 02/060812 by Tour et al., filed Jan. 29, 2002
and incorporated herein by reference. Using pre-synthesized
diazonium salts, or generating the diazonium species in situ,
reaction with such species has been shown to produce derivatized
SWNTs having approximately 1 out of every 20 to 30 carbons in a
nanotube bearing a functional moiety. Nevertheless, because of the
poor solubility of SWNTs in solvent media, such processes require
extraordinary amounts of solvent for the dissolution and/or
dispersion of the SWNTs (.about.2 U/g coupled with sonication in
most cases). See Bahr et al., Chem. Commun., 2000, 193-194,
incorporated herein by reference.
[0010] Another method by which carbon nanotubes can be
functionalized under solvent-free conditions has been developed.
See PCT publication application US03/122072 by Tour et al., filed
Jul. 15, 2003 and incorporated herein by reference. As extremely
large quantities are typically required to dissolve or disperse
carbon nanotubes, solvent elimination renders the processes more
favorable for scale-up. Such processes are also amenable to a wide
variety of chemical reactions and organic functionalizing
agents.
[0011] PCT publication WO 02/060812, by Tour, et al., further
discloses that, once the functional group is attached to the
sidewall of the carbon nanotube, standard polymerization techniques
can then be employed to grow the polymer from the functional group
in situ. That is, the functional group attached to the nanotube
could be used as a starting point for polymer growth. Such standard
polymerization techniques could be any of the standard known types,
such as radical, cationic, anionic, condensation, ring-opening,
methathesis, or ring-opening-metathesis (ROMP) polymerizations,
when appropriate groups are bound to the nanotubes. The functional
group attached to the nanotube would be a chemically active part of
the polymerization, which would result in a composite material in
which the nanotubes are chemically involved.
SUMMARY
[0012] It has been discovered that aryl halide (such as aryl
bromide) functonalized carbon nanotubes can be utilized in anionic
polymerization processes to form polymer-carbon nanotube materials
with improved dispersion ability in polymer matrices. In this
process the aryl halide is reacted with an alkyllithium species or
is reacted with a metal to replace the aryl-bromine bond with an
aryl-lithium or aryl-metal bond, respectively. It has further been
discovered that other functionalized carbon nanotubes, after
deprotonation with a deprotonation agent, can similarly be utilized
in anionic polymerization processes to form polymer-carbon nanotube
materials. Additionally or alternatively, a ring opening
polymerization process can be performed. The resultant materials
can be used by themselves due to their enhanced strength and
reinforcement ability when compared to their unbound polymer
analogs. Additionally, these materials can also be blended with
pre-formed polymers to establish compatibility and enhanced
dispersion of nanotubes in otherwise hard to disperse matrices
resulting in significantly improved material properties. The
resultant polymer-carbon nanotube materials can also be used in
drug delivery processes due to their improved dispersion ability
and biodegradability, and can also be used for scaffolding to
promote cellular growth of tissue.
[0013] The foregoing has outlined rather broadly the features of
the present invention in order that the detailed description of the
invention that follows may be better understood. Additional
features and advantages of the invention will be described
hereinafter which form the subject of the claims of the
invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] For a more complete understanding of the present invention,
and the advantages thereof, reference is now made to the following
descriptions taken in conjunction with the accompanying drawings,
in which:
[0015] FIG. 1 schematically depicts an embodiment of the invention
in which aryl bromide functionalized carbon nanotubes are used as
the origin for polymerization;
[0016] FIG. 2 schematically depicts another embodiment of the
invention in which aryl bromide functionalized carbon nanotubes are
used as the origin for polymerization;
[0017] FIG. 3 schematically depicts another embodiment of the
invention in which phenol functionalized carbon nanotubes are used
as the origin for polymerization;
[0018] FIGS. 4(a)-(c) schematically depict ring opening
polymerization processes that can be utilized in another embodiment
of the invention; and
[0019] FIGS. 5(a)-(b) are functionized SWNT that can be used in
embodiments of the invention.
DETAILED DESCRIPTION
[0020] The present invention relates generally to processes for
growing polymer chains via polymerization from the sidewalls of
functionalized carbon nanotubes, which will facilitate greater
dispersion in polymer matrices and greatly enhanced reinforcement
ability in polymeric material.
[0021] For the present invention, aryl bromide functionalized
nanotubes can be utilized that were made using the processes
disclosed in PCT publication application US03/22072 PCT or,
alternatively, by the processes disclosed in publication WO
02/060812. (See also Dyke, C. A.; Tour, J. M. "Solvent-Free
Functionalization of Carbon Nanotubes," J. Am. Chem. Soc., 2003,
125, 1156-1157 or Bahr, J. L.; Tour, J. M. "Highly Functionalized
Carbon Nanotubes Using in Situ Generated Diazonium Compounds,"
Chem. Mater. 2001, 13, 3823-3824 or Bahr, J. L.; Yang, J.;
Kosynkin, D. V.; Bronikowski, M. J.; Smalley, R. E.; Tour, J. M.
"Functionalization of Carbon Nanotubes by Electrochemical Reduction
of Aryl Diazonium Salts: A Bucky Paper Electrode," J. Am. Chem.
Soc. 2001, 123, 6536-6542; all of which are incorporated by
reference). Such functionalization reactions can involve
HiPco-produced individual carbon nanotubes (Carbon Nanotechnologies
Inc., Houston, Tex.). Alternatively, the carbon nanotubes can be
functionalized with other aryl halides bonded to the sidewalls.
Further alternatively, the carbon nanotubes can be functionalized
with a species having nucleation sites for the polymerization, such
as species having carbon, sulfur, oxygen, and nitrogen sites for
polymerization.
[0022] As reflected in FIG. 1, aryl bromide functionalized
nanotubes can be dispersed in a solvent with an alkyllithium
species (RLi), which can be, for example, provided as a
tetrahydrofuran solution of n-butyllithium. The concentration of
the solution can be in the range between about 0.1 and 1.0 mg/ml.
The nanotube material may then be allowed to settle and the excess
n-butyllithium solution optionally may be removed via canulation.
The remaining nanotube material may be washed, such as with three
portions of dry tetrahydrofuran, to thoroughly remove any residual
n-butyllithium. The nanotube material may then be dispersed in a
solvent, such as dry tetrahydrofuran.
[0023] After dispersion, a monomer, such as, for example, stryrene
is added to the reaction vessel. Other monomers can be utilized,
such as those selected from the group consisting of styrene,
acrylates, methyl acrylates, vinyl acetate, vinyl pyridines,
isoprene (such as 1,4-isoprene), butadiene (such as 1,3-butadiene,
2-methyl-1,3-butadiene, 2-methyl-1,4-butadiene), chloroprene,
acrylonitrile, maleic anhydride, and combinations thereof. The
concentration of the monomer is in the range between about 0.03 and
0.16 g/ml The temperature at polymerization is typically in the
range between about 0 and 50.degree. C.
[0024] An anionic polymerization process is employed utilizing the
functionalized carbon nanotubes and the monomer, wherein the
polymerization can be effected by an anionic initiator.
[0025] Upon completion of the anionic polymerization, the active
chain ends can be terminated with an appropriate terminating agent,
such as ethanol, acetaldehyde, trimethylsilyl chloride, or
combinations thereof. The average chain length of the polymer
bonded to the carbon nanotubes are generally in the range between
about 5 and about 1 million, and can more specifically be in the
range between about 1000 and about 1 million. After termination,
the reaction mixture may be diluted and filtered to remove any
large particulate. The filtrate can then be concentrated under
reduced pressure and precipitated into methanol. The resultant
powder can be collected via filtration and dried under vacuum to a
constant weight.
[0026] FIG. 2 reflects an alternative embodiment of the invention
in which a Grignard synthesis is utilized in lieu of reacting the
functionalized carbon nanotubes with the alkyllithium species.
Optionally, for such Grignard synthesis, a catalyst, such as
TiCl.sub.4, may be utilized during the polymerization process. Like
processes to this Grignard synthesis can be performed by utilizing
other metals that will react with the functionalized carbon
nanotube to convert the aryl-halide bond to an aryl-metal bond.
Such metals include zinc, nickel, potassium, sodium, lithium,
cesium, palladium, and combinations thereof (and also combinations
of these metals with Mg).
[0027] Furthermore, as an alternative to utilizing aryl halide
functionalized carbon nanotubes, carbon nanotubes functionalized
with a species having nucleation sites operable for polymerization
(such as species having carbon, sulfur, oxygen, and nitrogen sites
for polymerization) can be utilized. For example, phenol
functionalized carbon nanotubes, thiophenol functionalized carbon
nanotubes, phenethyl alcohol functionalized nanotubes
(CNT-C.sub.6H.sub.4--CH.sub.2CH.sub.2OH), and
CNT-C.sub.6H.sub.4--NHBoc can be used.
[0028] FIG. 3 reflects an alternative embodiment of the invention
in which phenol functionalized carbon nanotubes are utilized during
the anionic polymerization process to make the polymer-carbon
nanotube materials. Carbon nanotubes functionalized with species
having nucleation sites for polymerization, such as phenol
functionalized carbon nanotubes, are then treated with a
deprotonation agent to deprotonate the nucleation sites to form
initiator groups for polymerization. Such deprotonation agents
include bases (such as KOH, KH, NaOH, NaH, and potassium
hexamethyldisilazide (KHMDS)) and metals (such as zinc, nickel,
potassium, sodium, lithium, magnesium, cesium, palladium, and
combinations thereof) that will react with the functionalized
carbon nanotubes to deprotonate the functionalized species. After
deprotonatination, the anionic polymerization process can be
performed, such as in the manner described above.
[0029] The resultant materials of the anionic polymerization
processes may then be used as is or blended with other matrices to
obtain superior dispersion and reinforcement properties. For
instance nanocomposites thus synthesized using 1,3-butadiene can be
saturated to form tethered analogs of low density polyethylene that
form miscible mixtures with high density polyethylene resulting in
nanocomposites where nanotubes are dispersed in a HDPE matrix with
superior material properties. Similarly, starting from 1,4-isoprene
followed by saturation will lead to the formation of a strictly
alternating copolymer of ethylene and propylene that is compatible
with many commercial grades of ethylene--propylene elastomers.
Additionally, preparation of high vinyl butadiene based polymers by
polymerization in a highly polar solvent will lead to the tethering
of copolymers of 1,4-1,2 polybutadienes with high 1,2 content
resulting in compatibility with isotactic, syndiotactic and atactic
polypropylenes.
[0030] Some embodiments of the present invention involve a ring
opening polymerization utilizing a ring opening polymerization
initiator. For instance, ring opening polymerization of
.epsilon.-caprolactone is initiated by a number of different types
of catalysts utilizing various co-initiators such as alcohols,
carboxylic acids or amines. Mechanisms for the polymerization of
PCL are presented in FIGS. 4(a)-(c). Polymerization of
s-caprolactone proceeds by anionic (4(a)), cationic (4(b)), or a
coordination insertion type mechanism (4(c)) [Storey and Sherman,
"kinetics and Mechanism of the Stannous Octoate-Catalyzed Bulk
Polymerization of epsilon-caprolactone", Macromolecules, 2002, 35,
1504-1512]. Depending on experimental conditions and reagents used,
it is understood that that all three mechanisms may possibly occur
simultaneously. In the present Application, it is further
understood that the alcohol or acid functionality covalently bound
to the SWNT can thus act as nucleophile (via the conjugate base, as
in FIG. 4(a)) or can participate in forming the alkoxide that
initiates the polymerization as in FIG. 4(c). Polymerizations were
conducted under several experimental conditions: (i) in bulk at
130.degree. C. utilizing a tin octoate based catalyst [Storey and
Sherman, "Kinetics and Mechanism of the Stannous Octoate-Catalyzed
Bulk Polymerization of epsilon-caprolactone", Macromolecules, 2002,
35, 1504-1512] and either hydroxyl terminus or carboxylic acid
terminus functionalized nanotubes (see FIGS. 5(b) and 5(a),
respectively), (ii) in solution with toluene as the solvent at
100.degree. C. utilizing a tin octoate based catalyst
[Kowalski;Duda and Penczek, "Kinetics and mechanism of cyclic
esters polymerization initiated with tin(II) octoate, 1", Macromol.
Rapid Commun. 19, 1998, 19, 567-572 and either hydroxyl terminus or
carboxylic acid terminus functionalized nanotubes, (iii) acid
catalyzed ring opening at 170.degree. C. [Messersmith and
Giannelis, "Synthesis and Barrier Properties of Poly
(epsilon-caprolactone)-Layered Silicate Nanocomposites", Journal of
Polymer Science: Part A: Polymer Chemistry, 1995, 33, 1047-1057]
utilizing carboxylic acid terminus functionalized nanotubes, and
(iv) polymerization utilizing a tin octoate based catalyst and
pristine nanotubes in toluene or any other solvent.
[0031] The resultant materials of the ring opening polymerization
of .epsilon.-caprolactone, l-lactic acid, d-lactic add, glycolic
acid and copolymers of these to obtain superior dispersion,
reinforcement, and control micron and sub-micron scale structures
and maintain the biocompatibility and biodegradation
characteristics of the polymers. PLLA- and PLGA-based microspheres
have been used previously for drug delivery applications. Addition
of nanotubes and in particular tethering of the polymers to the
surface of the nanotube would result in materials with smaller
crystals, development of controlled micro or nano particles and
higher drug carrying capacity per mass of polymer. Traditional
polymeric scaffolds suffer from lack of mechanical integrity
particularly when foamed to produce microchannels for the transport
of nutrients, growth factors and possible vascularization. The
materials described here are mechanically reinforced by the
nanotubes and exhibit superior foaming properties resulting from
the intimate mixing and attachment of the polymers to the
nanotubes. These materials can also be blended with other polymers
and other nanoparticles such as gold nanoshells to provide
scaffolding and drug delivery mechanisms respectively.
[0032] In summary, the present invention provides for the anionic
or ring opening polymerization initiated at a functional group,
such as aryl bromide and other aryl halides, as well as other
carbon nanotubes functionalized with a species having nucleation
sites for the polymerization, on the sidewalls of carbon
nanotubes.
[0033] The following examples are provided to more fully illustrate
some of the embodiments of the present invention. It should be
appreciated by those of skill in the art that the techniques
disclosed in the examples that follow represent techniques
discovered by the inventors to function well in the practice of the
invention, and thus can be considered to constitute exemplary modes
for its practice. However, those of skill in the art should, in
light of the present disclosure, appreciate that many changes can
be made in the specific embodiments that are disclosed and still
obtain a like or similar result without departing from the spirit
and scope of the invention.
EXAMPLE 1
[0034] This Example illustrates the growth of a polymer chain from
the sidewalls of functionalized SWNTs in accordance with
embodiments of the present invention.
[0035] Aryl bromide functionalized single wall carbon nanotubes
(0.015 g, 0.022 mmol Br) are dispersed in THF (5 mL) and a solution
of n-butyllithium (5 mL, 2.19 M in hexane) was added at 23.degree.
C. and the solution was allowed to stir for 10 min. The stirring
was then turned off and the nanotubes were allowed to settle out of
solution. After settling, the excess n-butyllithium solution was
removed from the reaction vessel via cannula and the nanotubes were
washed 3 times with dry THF (10 mL) to remove unreacted
n-butyllithium.
[0036] The flask was then charged with dry THF (10 mL) and the
tubes were dispersed in solution with rapid stirring. Styrene (1.7
mL, 15 mmol) was added to the reaction vessel and the mixture was
stirred for 180 min before adding ethanol (1 mL) or a function
terminator of choice such as trimethylsilyl chloride. The mixture
was then diluted with 100 mL dichloromethane and filtered through
Fisherbrand P8 filter paper to remove any large particulate. The
filtrate was concentrated under reduced pressure and precipitated
into methanol. The resulting gray powder (product) was then
collected by filtration, using Whatman 41 filter paper and dried
under vacuum (0.1 mm) to a constant weight (typically, 0.100-1.00 g
depending on the precise amount of styrene added).
EXAMPLE 2
[0037] This Example illustrates the growth of a polymer chain from
the sidewalls of functionalized SWNTs via a ring opening
polymerization process in accordance with embodiments of the
present invention.
[0038] A flask was charged with dry toluene (100 mL) and
4-(10-Hydroxydecyl)benzoate functionalized SWNTs were dispersed in
the toluene with rapid stirring. .epsilon.-caprolactone (12 mL) was
added to the reaction vessel and the mixture stirred at room
temperature for 10 minutes. The amount of functionalized nanotube
was adjusted to achieve composites with 0.1 to 5 wt % nanotubes.
The solution was then placed in an oil bath and rapidly heated to
100.degree. C. and allowed to equilibrate for 15 minutes under
vigorous stirring. Tin octoate in stoichiometric equivalence to the
hydroxyl concentration was added and the reaction allowed to
proceed for 48 hours. The mixture was then cooled to room
temperature (23.degree. C.) and subsequently precipitated in
hexane. The samples were repeatedly dissolved in toluene and
precipitated in hexane to remove any excess monomer. The samples
(product) were then dried under vacuum (0.1 mm) at 80.degree. C.
for a minimum of 24 hours to a constant weight (within 0.01
grams).
[0039] All patents and publications referenced herein are hereby
incorporated by reference. It will be understood that certain of
the above-described structures, functions, and operations of the
above-described embodiments are not necessary to practice the
present invention and are included in the description simply for
completeness of an exemplary embodiment or embodiments. In
addition, it will be understood that specific structures,
functions, and operations set forth in the above-described
referenced patents and publications can be practiced in conjunction
with the present invention, but they are not essential to its
practice. It is therefore to be understood that the invention may
be practiced otherwise than as specifically described without
actually departing from the spirit and scope of the present
invention as defined by the appended claims.
* * * * *